Blueing stainless to prevent more heat discoloration 1

[stephenryan]

Hi everyone,
First question here and it may seem silly but ive ordered a new set of stainless headers for my exhaust (unsure of grade) but i know they will discolor to a nasty straw yellow over the heat. I would like to keep them clean but i know thats not possible.

My question is, if I blue the pipes with a blow torch carefully to a blue(ish) color, should that prevent any further color changes because it has gone through most the stages already or will it revert back after prolonged heat? (though not hot enough to turn blue naturally)

Thanks in advance

 

[Compositepro]

Stainless steel is protected by a transparent oxide layer from corrosion. Heat tint colors are caused by thickening of the oxide layer over time at high temperatures. The thicker blue layers are prone to cracking, resulting in a loss of corrosion protection. So I don't think that your idea is practical.

https://www.thefabricator.com/article/tubepipeproduction/keeping-stainless-steels-stainless

 

[EdStainless]

Option 1, live with it.

If you could heat them in air to a slightly higher temp than they will see in service, then they should stay that way.
The trick is that you need the oxide to be very thin. It will still be transparent and shinny even though it is blue-ish.
There are people out there that do this electro-chemically in an acid bath.
Once the oxide layer gets thick enough to be dull it is very detrimental to the parts.

The other option is to treat with something like this:

https://www.minimox.com/applications/oxidation-resistance/

This stuff goes on looking like dirty water, but it really suppresses the oxidation.

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P.E. Metallurgy, Plymouth Tube

 

[stephenryan]

Thanks for the input, very interesting.
@EdStainless, I dont think Ive ever seen stainless turn 'dull' before. You mean like a strong blue color like Ive mentioned or a physically dull surface finish with a bright light shining on it? I will look into Minimox
@Compositepro, very interesting. I didnt think of the oxide layer cracking. If it was to crack though, wouldnt the exposed steel just form a new chromium oxide layer, resulting in worst case scenario of streaks of silver thoughout the blue sections? Are you saying it would start to rust?

 

[EdStainless]

As the layer gets thicker then it is no longer transparent, and it gets dull brown, blue, purple, or black.
The issue with these thicker scales is that they are very porous, and they do crack sometimes even flaking off.
This is an issue because the metal then exposed has lower Cr content, because some of its Cr went into the scale.

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P.E. Metallurgy, Plymouth Tube

 

[SwinnyGG]

Are you saying it would start to rust?

Compromising the oxide layer can cause corrosion, yes. When you create that layer you're leaching alloying elements out of the base material, so if the oxide layer flakes off or gets scraped or whatever, the base material has a lower percentage of the alloying elements that provide corrosion protection.

I've never heard the color that stainless headers turn after heating described as 'nasty'. I find it no less appealing than the color of as-processed stainless tube, but that's personal preference.

If you want to keep them looking as-new, your best bet is coating them. There are commercially available options such as Cerakote that provide cosmetic benefits. You'll also get some (small) performance benefits from ceramic header coatings- they provide a layer of insulation, which keeps the exhaust gasses hotter and also can lower underhood temps by reducing the radiation of head from the header tubes.

 

[Compositepro]

That Minimox process does look very interesting.

 

IC exhaust is hot and nasty; your headers won't stay shiny for long.
Do you visually admire your headers while driving?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[IRstuff]

Better yet, use your beater to tow your nice car around; that way, the headers will always be shiny, assuming you polish them night before the autoshows.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[stephenryan]

Wow this is super informative. I had a really simplistic view of metallurgy before now.
All of this makes sense though so coating is definitely the way to go since I now wont be destroying several hundred euros worth of equipment!

@ironic metallurgist Its for my motorcycle and yes I do sit and admire my headers, I am that anal

I also assume that this applies to sanding & polishing to remove the tarnished color (as countless of us bikers do, in my circles anyway). Wont be doing that anymore.

Thanks again for warning me off, never been so relieved to be told Im wrong!

 

[EdStainless]

What happens when you sand and polish is that the oxide ends up getting embedded into the surface.
If the headers are always dry it is no big deal.
But if the bike sits cold in a humid environment you are likely to start getting rust spots on them if you have done this.
A lot of aircraft application like headers that are either chemically pickled or bead blasted. They have a nice light colored matte finish and the discoloration is less noticeable.

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P.E. Metallurgy, Plymouth Tube

 

stephenryan,
Thanks for taking it in the spirit it was intended. We don't want to discourage civilians coming here with real-world questions.
As you gathered by now, stainless steel surface finish is a complicated question that preoccupies a lot of us.
Post a picture of your ride here if you have one handy.
IM

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dgallup]

There are lots of outfits like Jet Hot that will be glad to ceramic coat your headers. I did that on my motorcycle header and it still looks good 12 years later.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Compositepro]

Platinum or gold plating should work.

 

[EdStainless]

Stephenryan,
Thanks for staying with the discussion.
As I mentioned there are people that use the combination of an acid bath and electricity to create tint films on stainless steel.
Here is an example:

https://millenniumforms.com/options/colors

This might be interesting to explore.
Regards, Ed

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P.E. Metallurgy, Plymouth Tube